BIOACCUMULATION OF MERCURY IN LARGE CATFISH OF THE COOSA RIVER, GEORGIA

Bioaccumulation of mercury within fish is a well-documented occurrence. Once mercury (from diverse sources) reaches water, it is converted into methylmercury, a potent and widespread neurotoxin. Fish then absorb methylmercury from water passing over their gills and from their food. The mercury then binds itself to proteins found within the fish tissues. This can be devastating to piscivorous wildlife and humans. Once the fish tissue is ingested by humans, the mercury has the potential to damage the nervous system, especially in young children and pregnant and nursing women. More than 80% of human fish consumption advisories throughout the nation are due to mercury in fish. Each year, the Georgia Department of Natural Resources publishes "Guidelines for Eating Fish From Georgia Waters," which is based on eating fish at similar contamination levels for a period of 30 years or more. While this is a comprehensive document, it does not specifically mention large fish (>30 pounds). The largest size fish in reservoirs falls into the "over 16 inches" category and guidelines for streams and rivers are based on the common creel size. It is expected that older, larger fish would likely have greater concentrations of mercury within their tissues, thereby posing a greater risk to humans. Fish species chosen for inclusion in this study were large blue catfish and flathead catfish, since they feed on the bottom. Bottom feeders are directly in contact with contaminated sediments or invertebrates that live in the sediment, thereby making accumulation more likely. Sampling occurred during the summer of 2004, when lipid contents of the fish are higher. Fish were caught in the Coosa River basin, along Big Cedar Creek in the Weiss Reservoir in Floyd County, Georgia, adjacent to Alabama. Field parameters were measured at each catch. All fish samples were handled according to EPA guidelines for fish sampling for bioaccumulative contaminants. Composite samples of fish were utilized in order to obtain information on average contaminant concentrations. Samples were frozen and sent to an independent laboratory for total Hg analysis. In Rome, Georgia, just upstream of the sampling location, mercury levels of 0.125, 0.027, and 0.03 µg Hg/g wet weight and 0.653, 0.153, and 0.163 µg Hg/g dry weight have been recorded in black crappie (Brumbaugh et al., 2001).